Electric furnace.



J. M. LOHR I -H. W. GILLETT.

ELECTRIC FURNACE.

APPLICATION FILED Ausm, 1915.

1 1 62, 1 78, Patented Nov. 30, 1915.

2 SHEETS-*SHEET l.

COLUMBIA PLANDGRAPH Ca. WASHINGTON. u. cA

J. M. LOHR & H. W. GILLETT.

ELECTRIC FURNACE.

APPLICATION FILED AUG.31, 1915.

1,162,178. Patented Nov. 30, 1915.

2 SHEETS-SHEET 2.

Znvenofsx UNITED STATES VPATENT JAMES M'. LOIIR AND HORACE W. GILLETT, OF ITHACA, NEVI YGBK.

ELECTRIC FTENACE.

Application filed August 31, 191

Speccation of Lette 's Patent.

Fat-entera ov. 3Q, li.

Serial No. 43,337.

(DEDICATED T)V THE PUBLIC.)

'the following is a specification.

This application is made under the act of March 3, 1883, c. 148, (U. S. Stat., 22, p. 625) and the invention described herein may be used by the Government of the United States, or any of its-ofiicers or employees in the prosecution of the work of the United States or by any person in the United States without payment of any royalty thereon.

This invention relates to electric furnaces and more particularly to multiple crucible liftout furnaces which may be used for melting substances such as brass and other alloys, or for heat treatment of'metals and alloys.

One object of our invention is to so arrange the heating elements in the furnace that the maximum part of the heat developed will be imparted directly to the substances to be heated.

Another obj ect is to keep the furnace walls as cool as possible to prevent their deterioration and economize heat.

Another object is to avoid the losses of heat energy which occur in the operation of prior furnaces.

Still another object is to edect these gainsV in efficiency while permitting easy access to the interior'of the furnace to permit ready removal or manipulation of the heated material.

Another aim is to provide a furnace which may be adapted to existing fuel fired crucible furnaces.

Other objects will appear from the following description. i

In the accompanying drawings Figure 1 is a plan view of one form of the invention with the furnace covers removed. Fig. 2 is a vertical longitudinal section thereof; Fig. 3 is a plan view of another form of the invention. Figs. 4 and 5 are plan views of still further modifications and Figs. 6, ",y

and 8 are diagrams illustrating different electrical connectionsfor the furnaces.

Referring to Figs; `1 and 2,the furnace comprises a casing 1 of any suitable refractory material, the casing being elcngater so as to contain a series of spaced apart crucibles of any preferred shape. Transversely of the furnace between the crucibles and spaced therefrom are heating elements 5 and 6 which are here shown conventionally as -carbon resistors but may be granular resistors of carbon or graphite in refractory troughs, plate resistors, second class conductors like silicon carbid with auxiliary starting heaters, or any other electric heaters including even arcs. The resistors divide the furnace into compartments in the bottom of each of which is a refractory spacer 13, such as a fire brick, which is smaller than the bottom of the Crucible to allow a. lifting device to engage the bottom of the crucible. This spacing means may be used in all species of our invention. There is sufficient space between the crucibles and the walls and resistors in all forms of our furnace to permit the use of bottom engaging lift-ing devices. The resistors 5 and 6 are shown in Fig. 1 connected in series within the furnace by a refractory conductor 7, which may be made of graphite. Power is derived from conductors 8 and 9. YVhen desired the resistors may be connected in parallel. Either direct or alternating current may be used. Fig. 6 indicates one way of connecting the resistors 5 and 6 to a source B of two phase alternating current, the Scott connection being employed at source B.

In all forms of the furnace suitable removable refractory covers 10 and 11 may be used.

Fig. 3 shows a furnace similar to that of Fig. 1 except that the casing 12 is prolonged to contain four crucibles 13, 14, 15, 16 andvthree resistors 17, 18, 19. rThe three resistors and the power lines 22, 23 are connected in series by connectors 20, 21 outside of the furnace. The outside connection makes'the structure more simple but slightly increases the heat loss by conduction through the projecting resistor ends.

Fig. 7 shows how the resistors 17, 18, 19 may be connected in delta from a source C of three phasel alternating current.

The form of furnace shown in Fig. @l includes a substantially triangular casing 24 divided into four compartments by a triangular resistor composed of sides 29, 30, 31.

sol

Crucibles 25, 26, 27, and 28 are centrally disposed in these compartments. This triangular resistorris shown as connected in delta Y ors 43, 50, 52 which together with the outerV connectors 49, 5l join the resistors in series `with the power line wires 53 and 54. `Any other connection may be used, if necessary, to adapt the furnace tothe particular electric power service that is available.

`Tn Fig. 8 the resistors are joined in delta to a source D of three phase current. Gf course a star connection could be substituted in Figs. 7 and 3. Y

Tn all forms of the furnace suitable resist-V ance to regulate the current may be interpc ed .if desired.

Tt Y is an essential characteristic of all forms of our furnace that each side of every resistor radiates heat directly to a heating chamber containing a crucible or other object to be treated. ln other words no resistor radiates heat directly to a side wall of the furnace without the interposition of a Crucible or other material to be heated between the resistor and wall. For example in the furnace Vshown in Figs. l and 2 approximately one half of the heat from resistor 5 is radiated to Crucible 3 and the other half to crucible 2. Similarly the heat from resistor 6 is divided between crucibles 3 and 4. Tn this particular form'the speed of heating of the end crucibles 2 and 4 may be less than that ofthe middle Crucible` 3 which receives heat from both resistors. If the speed of heating in the end chambers is not suflicinet, they may be used as preheatving chambers, the preheated material being transferred when ready to the middle chamber. v

In thefform of furnace shown inFig. 5 there are no end chambers so that every chamber is heated by direct radiation from two resistors. VThis furnace vmay be constructed from existing-types of fuel fired furnaces that are arranged about a central stack, the refractory walls of the combustion .Y furnace bein@ readily adapted to the electric furnace.

This not only causes;

deterioration of the walls but results in great waste Vof energy. Tf the furnace is running continuously large amounts ofwaste heat are conducted through the walls and if the furnace is run intermittently large quan- Y tities of heat are uselessly employed in heating up the cooled walls at the beginning of l each heating operation.

Tn our furnaces on the contrary, the walls are only indirectly heated and are at a much lower temperature. This diminishes the heat lost through the walls in continuous runs, and greatly lessens losses of energy in ieheating the walls durin-g intermittent runs. The furnace temperature is more easilyregulated in consequence andthe walls are more durable. The energy supplied to our furnaces for heating a given amount of material is therefore much less than (in some instances only half of) the energyconsumed in usual types of crucible furnaces.

Tn the preferred 'form of our invention, the .crucible chambers are practically uniform in size so that a predetermined size of Crucible may be used interchangeably in all chambers.

l'Thile we have referred to the radiation of the heat to the ciucible or material tor be heated, it isv apparent that part of the heat may also be carried from the resistors to the crucibles by convection without affecting the efficient operation as above set forth.

It will be noted that the number of chambers in furnaces employing our invention may vary from two chambers with one resistor between them up to any convenient number.

'nients dividing said casing into chambers,

each heating element'being locatedfbetween two chambers so asto radiate heat directly into said chambers, the casing'beingonly indirectly heated. y

2. An electric furnace comprisinga casing andv spaced Crucibles-therein, electric heating elements located between and spaced from said crucibles so as to transmit heat directly to said crucibles andvonly indirectly to said casing.

3. YAn electric furnace comprising a casing, a closed or endlessseries of spaced crucibles therein, and electric heating elements located between the crucibles each heating element transmitting directly'to two adja- Cent-cruCibleS. Y

4.4 An electric'furnace comprising an annularl troughshaped casing, an annular series of crucibles therein, and electric'heatsoV ing elements located between the crucibles, each heating element radiating heat directlyv to a Crucible on each side of it.

5. An electric furnace comprising a easing, a series of erucibles therein spaced from each other and from the casingteleotric heating elements between but spaced from said cruoibles, spacing means on the bottom of Said casing of less area than the bottom of any Crucible, whereby space is provided beneath and at the sides of said erucibles for manipulating and lifting the same. JAMES M. LOHR. HORACE W. GILLETT.

Copies of this patent may 13e obtained for ve cents each, by addressing the Commissioner of Patents, Washington, I). C. 

